Question 4. What are the advantages of sexual reproduction over asexual reproduction?

Answer.

Sexual reproduction in different modes ensures diversity in the ecosystem

In sexual reproduction, inbuilt tendency for genetic variation , plays an important role in the origin of new
species and forms the the basis for evolution

Variation resulting from sexual reproduction, is useful for the survival of species over time

Sexual reproduction is also linked to stability of populations of species

Question 5. What are the functions performed by the testis in human beings?

Answer. The testis is the main organ of male reproductive system in human beings. The formation of germ-
cells or sperms takes place in the testes. These are located outside the abdominal cavity in scrotum
because sperm formation requires a lower temperature than the normal body
temperature. The testes produces germ cells or sperm. They secrete a hormone called testosterone,
which, regulate the formation of germ cells or sperms and also helps in development of secondary sexual
characteristics as seen in males at the time of puberty. The sperms so formed are tiny bodies that consist of
mainly genetic material and a long tail that helps them to move towards the female germ-cell.

Question 6. Why does menstruation occur?

Answer. In Human–female reproductive system, the ovary
releases one egg every month, during the same period, the uterus also prepares itself
to receive a fertilised egg. Thus its lining becomes thick and spongy.
This would be required for nourishing the embryo if fertilisation had
taken place.

If the egg is not fertilised, it lives for about one day and then it is lost. The lining
earlier formed to receive the fertilised egg, is not needed any longer. So, the
lining slowly breaks and comes out through the vagina as blood and
mucous. This cycle takes place roughly every month and is known as
menstruation. It usually lasts for about two to eight days

Question 7. Draw a labelled diagram of the longitudinal section of a flower.

Answer.

Question 8. What are the different methods of contraception?

Answer. The different methods of contraception are :

Mechanical barrier : Creation of a mechanical barrier so that sperm does not
reach the egg. This can be achieved with a condom which is worn around the penis or a similar device that is
placed in the vagina. Intra uterine devices such as copper-T can also be used, however they may cause side effect
in the form of uterus irritation.

Chemicals : Contraceptives pills containing special chemicals, when taken orally, acts
by changing the hormonal balance of the body so that eggs are not
released and fertilisation cannot occur. However, since they change hormonal
balances, they can cause side-effects too.

Surgical : If the vas deferens in the male is blocked through Surgical methods like vasectomy, sperm
transfer will
be prevented. Similarly, if the fallopian tube in the female is blocked through Surgical methods like tubectomy,
the egg will not be able to reach the uterus. In both cases fertilisation will not take
place.

Question 9. How are the modes for reproduction different in unicellular and
multicellular organisms?

Answer. Unicellular organisms have just one cell. There are no specialised tissue for reproduction. So for
reproduction they make use of asexual methods such as binary fission, budding, multiple fission, etc.
Multicellular organisms,on the other hand, as they are made up of simple cells as well as of complex tissues and
organs with specialised function, use both asexual and sexual methods for reproduction.Simple organisms employ the
asexual methods of reproduction; where as most of the multicellular organisms utilise sexual methods of
reproduction.

Question 10. How does reproduction help in providing stability to populations of species?

Answer.
In an ecosystem, populations of species, use their ability of reproduction to occupy a well-defined places, or
niches. The consistency of DNA copying during reproduction is important for the maintenance of body
design features that allow the organism to successfully adopt to that particular niche for survival.
Every species and its member for its survival, struggle for food and place of habitat. Natural predators which
form the echo chain and extremities of nature keep on depleting large chunk of population of species on continuous
basis. Apart from these, death at the end of the natural life cycle of a species consumes its population on continuous basis. To over come this continuous loss of populations in diverse species, reproduction is very
important and essential. Thus, it can be said that reproduction is linked to the stability of population of a
species.

Question 11. What could be the reasons for adopting contraceptive methods?

Answer.
Since the beginning of human age on this planet, the human population, has increased manifolds. In recent times,
due to unplanned human reproduction, this ever increasing size of the human population, has resulted in creating
pressure on life supporting resources such as food, air, water, fuel and habitat which are limited and are are
facing continuous depletion or contamination. Due to this living standards of human beings are likely to degrade
further. Now the population growth is a cause for concern at individual level as well as, at community level.
At community level, adopting different contraceptive methods, may check population growth. Which will result in
better basic health care, education and economic conditions for the community members.
Similarly, at personal level, adopting contraceptive methods will not only will limit the number of children but
also help in maintaining the gap between children births. This will ensure improved over all living standards for
the family and good up bringing of children.

Answer. The creation of a DNA copy is a basic and an important event in reproduction. Organisms appear to
be same because of similarity in their inherited body designs. DNA in the cell nucleus, contains the blueprint of
body design and information for inheritance of characteristic features from parents to next generation. During
Reproduction, as the cell divides, a copy of DNA along with additional cellular apparatus , is transferred from the
parent cell to its offspring.
DNA copying mechanisms supports life sustaining process with replicating encoded genetic instructions in new
cells. Some minor changes during DNA copying result in bringing variations which are useful for ensuring the
survival of the species in long run.

Question 2. Why is variation beneficial to the species but not necessarily
for the individual?

Answer. The process of copying the DNA will have some variations each time. As a result, the DNA copies
generated will be similar, but may not be identical to the original. The surviving cells are similar to, but
subtly different from each other. Sometimes these variations are so drastic that the new DNA
copy cannot work with the cellular apparatus it inherits. Such a newborn
cell will simply die. On the other hand, there could still be many other
variations in the DNA copies that would not lead to such a drastic
outcome.This inbuilt tendency for variation during reproduction is the basis for evolution of new species.
variation beneficial to the species but not necessarily
for the individual

Answer.Binary fission : Some unicellular organisms under favourable conditions simply split into
two equal halves during
cell division. This is called binary fission. Examples are different bacteria and protozoa such as AmoebaMultiple Fission : Some organisms like the malarial
parasite, Plasmodium, divide into many daughter cells simultaneously. This process division is called multiple
fission.

Question 2. How will an organism be benefited if it reproduces through spores?

Answer. The spores are covered by thick walls of tiny blob-on-a-stick like structures, which are not
reproductive parts, but protect the spores from unfavorable conditions, until they come into contact with another
moist surface and can begin to grow. Such spores are produced in large numbers and can spread through air, water
or animals in contact. They germinate when favorable conditions return Thus, organism like Rhizopus is benefited
greatly when it is produced through spores

Question 3. Can you think of reasons why more complex organisms cannot give
rise to new individuals through regeneration?

Answer. More complex organisms cannot give rise to new individuals through regeneration because :
Complex organism are made up of Multi-cellular organisms. In complex organisms, specialised cells are organised
as tissues, and tissues are organised into organs, which are strategically placed to perform different
specialized functions. The tissues in complex organisms cannot regenerate a new individual as cell-by-cell
division would be impractical. For example, human hair cannot regenerate into a new individual as it is a highly
differentiated tissue performing a special function.
In plants which do not produce viable seeds it is the only method of reproduction.
b. Vegetative propagation is quicker and mature plants can be raised very quickly by this method.
c. Genetically similar plants can be produced. This is of great importance in agriculture and gardening.

Question 4. Why is vegetative propagation practised for growing some types of
plants?

Answer. Some plants like banana, orange,
rose and jasmine, can not be propagated through seeds as they do not produce viable seeds. In such plants, the
propagation of plants is done through vegetative propagation, in which new plants are produced under ideal
conditions, using their parts like the root, stem and leaves . Plants raised by vegetative propagation can bear
flowers and fruits earlier than those produced from seeds. Another advantage of vegetative propagation is that all
plants produced are genetically similar in characteristics to the parent plant.

Question 5. Why is DNA copying an essential part of the process of reproduction?

Answer. DNA copying is a basic and an essential event in reproduction. Organisms appear to be same because
of similarity in their inherited body designs. DNA in the cell nucleus, contains the blueprint of body design and
information for inheritance of characteristic features from parents to next generation . During process of
reproduction, as the cell undergo division, they use chemical reactions to build copies of their DNA. In the absence of a cellular apparatus, creation of DNA copies alone can not sustain the life process further. Therefor,
DNA copying is accompanied by the creation of an additional cellular apparatus, and then the DNA copies separate,
each with its own cellular apparatus. In this way, a cell divides in to two cells, each of which are capable of
supporting life process further. DNA copying mechanisms creates variations which are useful for ensuring the
survival of the species in the long run.

Answer.Pollination : The process of pollination involves transfer of a pollen grain from an anther
to a stigma in flowering plants (Angiosperms type) or to the area of the ovule in more primitive, non-flowering
plants such as ferns ( Gymnosperms Type ). This transfer of pollen grain may be with in the same flower, flowers
of same plant or different plants. Air, water and animal movements facilitate the process of pollination. In this
process, no fusion of two cells takes place.Fertilisation : In this process, actual fusion of two cells in the form of male gamete and the female gamete
takes place and result in the formation of zygote.

Question 2. What is the role of the seminal vesicles and the prostate gland?

Answer.Seminal vesicles and the prostate gland form the part of the accessory glands, which are associated
with the male reproductive system. Seminal vesicles and prostrate gland secrete a fluid which makes the transport
of sperms easier along the path of urethra and at the same time provides nutrition to the sperms. This secreted
fluid together with the sperms is called semen. -

Question 3. What are the changes seen in girls at the time of puberty?

Answer.At the time of Puberty, which generally sets in between 8 to 13 years of age, the following
changes can be seen in the girls :

Enlargement of breasts

Hair growth in the genital region and under the arms.

Change in Voice, body weight and shape

Change in emotions

Onset of menstruation cycle .

Question 4. How does the embryo get nourishment inside the mother’s body?

Answer. During the fertilisation process, the zygote is formed and gets implanted in the
lining of the uterus, and starts dividing to form the embryo. The growth of embryo is supported with thickening of
uterus lining and increased supply of blood.
The embryo gets nutrition from the mother’s blood with the help
of a special tissue called placenta. This is a disc which is embedded in the
uterine wall. It contains villi on the embryo’s side of the tissue. On the
mother’s side are blood spaces, which surround the villi. This provides
a large surface area for glucose and oxygen to pass from the mother to
the embryo. In this way, the embryo get nourishment inside the mother’s body
In addition to this, the placenta
also removes waste substances generated by the developing embryo by transferring them into the mother’s blood.

Question 5. If a woman is using a copper-T, will it help in protecting her from
sexually transmitted diseases?

Answer. No, copper-T is just a method of birth control. It will not help in protecting a woman from
getting sexually transmitted diseases which include bacterial infections
such as gonorrhoea and syphilis, and viral infections such as warts and HIV-AIDS. Due to nature of act, possibility
of disease infection, through contact or fluid exchange, will always be there. For protection use of condom is
strongly advisable.

Observation : During the week, on observing the surface of the slice with a magnifying glass, a layer
of white cotton like mass is seen covering the surface of slice. Area of white mass coverage found to be increasing on
subsequent days. After a weak, layer of white cotton like mass turns black showing formation of sporangia or
spores.

Observation : In the permanent slide of amoeba, an amoeba cell is seen containing normal cytoplasm and
nucleus. In permanent slide showing binary fission, nucleus seen to be dividing and the constriction is also seen
in cytoplasm, suggesting formation of two daughter' nuclei as shown in the figure.